1. Field of the Invention
The present invention relates to a micromotor capable of being disposed in a limited space in measuring instruments and medical instruments.
2. Description of the Prior Art
A conventional miniature permanent-magnet motor is shown in FIG. 6 by way of example and has a rotor formed by fixedly mounting a permanent magnet 9 on a shaft 8, and stator coils 4 fixed to the inner circumference of a motor frame so as to surround the permanent magnet 9 with an air gap therebetween. The shaft 8 is journaled in oil less bearings 6 fixed respectively to the opposite end plates of the motor frame.
A micromotor having the same construction as that of the foregoing miniature permanent-magnet motor and designed simply by scaling down the miniature permanent-magnet motor is unable to produce a sufficiently high torque and is liable to be heated to an excessively high temperature due to its inefficient heat radiation.